Ester interchange catalysts



ESTER INTERCHANGE CATALYSTS John Harris Hasiam, Landenberg, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware N Drawing. Application October 26, 1956 Serial No. 618,451

9 Claims. (Cl. 260-4483) This invention relates to ester interchange reactions involving silicon esters, and more particularly it relates to a new and improved method for the catalysis of these reactions.

Ester interchange reactions broadly comprise the reaction of an ester with an alcohol or another ester to form a different ester than the reactant ester. Such reactions include those esterification reactions heretofore commonly referred to as alcoholysis, re-esteriflcation, trahs-esterification, ester interchange, and ester disproportionation reactions. This invention relates specifically to such reactions as applied to silicon esters. Such reactions are known, and an example of such a reaction is an ester interchange between a silicon ester and a carboxylic acid ester to yield two new esters. Another example is'the reaction between an ester and an alcohol to form a new ester and to liberate an alcohol.

The silicon esters used in this invention are those compounds of silicon in which at least one of the valences is occupied by an alkoxy or aryloxy group. An orthoester of silicic acid would have four such alkoxy or aryloxy groups attached to the silicon, e. g., tetraethyl silicate. However, other silicon esters have some of the valences of the silicon occupied by hydrocarbon groups. An example of this type of compound is dimethyl diethoxy silane. Both types of esters discussed above are within the scope of this invention. It is known that such esters may be modified by the so-called trans-esterification reactions with which this invention is concerned. However, it has been well recognized that such reactions are inclined to be quite slow and to be ditficult to carry to completion. Furthermore, it has been proposed to use certain catalysts to improve the efliciency of these reactions. For instance, one may call attention to a paper by D. F. Peppard, W. G. Brown and W. C. Johnson in J. Am. Chem. Soc. 68, 77 (1946) under the title Transesterification Reactions of Alkyl Silicates. The authors have shown that certain reactive metal alkoxides, such as alkoxides of aluminum, magnesium and antimony, as well as aluminum chloride, improve the efliciency of such reactions. They also cite a number of trahs-esterification reactions and include in a table the time and the percent of reaction for many of these. in many of these examples, the reactions have proceeded to considerably better than 90% of completion, but the times involved range from about two hours up to as much as fifteen hours to obtain satisfactory completion.

It is an object of this invention to provide a new and improved method for the catalysis of ester interchange reactions involving silicon esters whereby such reactions are speeded up at lower temperatures, objectionable side reactions are reduced, and pure products are obtained.

The object of this invention may be accomplished by conducting an ester interchange reaction between a SLllCOIl ester and an organic compound selected from the group consisting of alcohols and esters of carboxylic acids in the presence of a catalytic amount of an organic titanium ester.

ateht Patented Jan. 21, 1953 grams of tetraethyl silicate (tetraethoxy silane) and 200 grams of h-butanol were placed in a boiling flask under a distilling column. On heating to full reflux, the head temperature remained at 116 C. for 20 minutes indicating the simple refluxing of the butanol. 5 ml. of tetra-lsopropyl titanate was then added to the flask. Almost immediately, the head temperature dropped to 77 C. and ethanol was taken oil at a maximum rate of 72 milliliters per minute until the head temperature again rose to 116 C. There was recovered 89.8 grams of liquid boiling at about 77 C. and comprising 86.6 grams or' ethanol and 3.2 grams of isopropanol derived from the tetraisopropyl titanate used. This corresponds to about 98 /o conversion of tetraethyl silicate to tetrabutyl silicate.

Example 11 74.1 parts (0.5 mol) of dimethyl diethoxy silane, 74.1 parts (1 mol) of n-butanol and 4.6 parts of tetraisopropyl titanate were charged to the same fractionating still as used in Example 1. On heating to reflux, there was re,- moved rapidly by suitable fractional distillation 4-8 parts of ethanol (approximately theoretical amount) at the normal temperature of 77 C. The residue was identified as dimethyl dibutoxy silane. B. P. 186-188 C.

Example 111 In a similar manner, 7.4 parts of dimethyl diethoxy silane, 11.6 parts of butyl acetate and 0.5 part of tetraisopropyl titanate were added to a suitable fractionatmg still. When distillation was begun, 8.1 parts of ethyl acetate was removed at 77 C. This constitutes about 92% of theory and the residue was identified as substantially pure dimethyl dibutoxy silane.

Example IV 178 parts of methyl triethoxy silane, 222 parts of n-butanol and 8 parts of tetrabutyl titanate are charged to a suitable fractionating still and heated to reflux tem perature. Alter a brief reflux period, the head temperature is 77 C. indicating that the refluxing liquid is ethanol and by a suitable rractional distillation through the column approximately parts of ethanol are removed (substantially the theoretical amount). The residue in the flask has a boiling point of about 115 C. at 10 mm. mercury pressure which indicates that it is substantially pure methyl tributoxy silane.

Example V 208 parts of tetraethyl silicate and 240 of n-propanol are added to the fractionating still together with 5 parts of tetraisopropyl titanate. 0n heating to reflux, 180 parts (substantially theoretical) of ethanol is removed at about 77 C. The material remaining in the flask is identified at tetra-n-propyl silicate with a boiling point of 225227, C.

Example VI 148 parts of dimethyl diethoxy silane and 186 parts of phenol are added to the fractionating column together with 7.5 parts of tetraphenyl titanate. On heating to butyl titanate, and effecting the ester interchange reaction.

8. In a process for conducting an ester interchange reaction between a silicon ester and an alcohol, the improvement which comprises incorporating with the reactants a catalytic amount of tetrabutyl titanate, and effecting the ester interchange reaction.

9. In a process for conducting an ester interchange reaction between a silicon ester and an organic compound selected from the group consisting of alcohols, phenols and esters of carboxylic acids, the improvement which comprises incorporating with the reactants a catalytic References Cited in the file of this patent UNITED STATES PATENTS Rothrock Mar. 10, 1942 Gresham Mar. 3, 1953 OTHER REFERENCES Peppard et al.: Jr. Am. Chem. Soc., vol. 68 (1946), pp. 77-79. 

1. IN A PROCESS FOR CONDUCTING AN ESTER INTERCHANGE REACTION BETWEEN A SILICON ESTER AND AN ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALCOHOLS, PHENOLS AND ESTERS OF CARBOXYLIC ACIDS, THE IMPROVEMENT WHICH COMPRISES INCORPORATING WITH THE REACTANTS A CATALYTIC AMOUNT OF A TITANIUM ESTER HAVING THE STRUCTURAL FORMULA TI(OR)4 WHERE R IS A HYDROCARBON RADICAL, AND EFFECTING THE ESTER INTERCHANGE REACTION. 